This invention relates to adsorbents, to a process for the production thereof and to the use thereof.
Adsorptive processes are today widely used for working up process solutions, for recovering valuable materials from production solutions and for treating exhaust air and waste water. Since the requirements for the purity of production solutions, for the recovery of valuable materials and for admissible exhaust air emissions and waste water loadings are becoming ever more stringent, there is a permanent requirement for further and new development of existing adsorption technologies.
The suitability of the adsorptive process is determined by adsorber properties such as selectivity, adsorption capacity, limitation of mass transport and the service life of the adsorber.
Adsorbers based on activated carbon or polymers as well as inorganic adsorbents are today primarily used for performing adsorption from the aqueous phase or from the air. Activated carbon is a highly porous, active carbon framework which consists primarily of carbon and small quantities of chemically bound oxygen and hydrogen. Activated carbon is distinguished by very large specific surface areas in the range from 500 to 1500 m2/g. The pore structure primarily consists of micro- and macropores, for which reason activated carbon is particularly effective at adsorbing molecules of a molecular weight of less than 200 Da. The specific total pore volume of activated carbon is generally 1-1.5 ml/g.
The strongly hydrophilic behaviour of the surface of activated carbon has a negative impact on its adsorption ability.
Wetting of the surface with water (molecules) reduces adsorption capacity for organic, non-polar molecules. Moreover, the maximum possible size of molecule which can be adsorbed on activated carbon is limited due to the micro- and submicropores. The macro- and microporous polymer adsorbers which are now available and consist, for example, of styrene/divinyl copolymers and have specific surface areas of between 400 and 1400 m2/g are one alternative to activated carbon. Depending upon the polymer and the surface modification, these polymer adsorbers exhibit hydrophobic or hydrophilic behaviour. Optimally adsorbed molecular masses are, however, frequently below 1000 Da.
Rubber powders (for example powdered rubber) containing fillers are also known (DE 199 24 367.0). These are obtained by acid-catalysed coagulation of a polymer emulsion in the presence of a filler suspension.
Granulation processes are known, in which carbon black powders were granulated by means of a granulation auxiliary in a pelletising machine (DE 196 23 198 A1, DE 197 56 501 A1, U.S. Pat. No. 4,222,727, U.S. Pat. No. 4,789,321, U.S. Pat. No. 3,787,161).
Production of these products is associated with disadvantages. Since the powders are produced from an aqueous phase comprising filler particles and polymer droplets, the surface of the filler is partially covered with the polymer. As a consequence, this surface area is no longer available for adsorbing pollutants.
An object of the present invention is to provide a readily applicable and effective adsorbent which makes the majority of the surface available for adsorbing pollutants.